Procedure for obtaining encryption keys, terminal, server and computer program products corresponding

Process for obtaining at least an encryption key of at least some data transmitted from a client to a characterized server comprising: - a step of determining an R number of registers available within said client to perform a plurality of calculations of keys encryption; - a step of determining a maximum N number of iterations required in obtaining at least an encryption key on that server; - a step of obtaining a data structure representing the state of key calculation performed within these R logs available; - a step of calculating said at least one key encryption function: - of the number of available registers R of said client, - making maximum N calls to a function F pseudorandom and - said data structure; so that said at least one encryption key may be obtained from a combination of up encryption keys from a preshared secret between said server and said client.